The present invention relates generally to warewashers which are used in commercial applications such as cafeterias and restaurants, and, more particularly, to a system for detecting jams which may occur in such warewashers.
Commercial warewashers commonly include a housing area which defines the washing and rinsing area for dishes, pots pans and other wares. A conveyor is used to transport the wares through the warewasher from an input side to an output side. At the output side of the warewasher a ware receiving table/trough may extend several feet to allow cleaned wares to exit from the warewasher completely before being removed by kitchen personnel.
One potential problem with such warewashers is that improperly loaded wares or ware racks can shift during conveyance through the warewasher to a position which causes a jam in the conveying system. In this type of jam condition the mispositioned ware or rack physically prevents movement of the conveyor, and damage to the warewasher itself can occur.
The prior art includes techniques which attempt to account for this jam condition. For example, as shown in FIG. 9, one prior art drive arrangement 200 includes a drive motor assembly 202 which is attached to a pivotable motor mount 204. The output of the drive motor assembly 202 is connected to a coupler 206 having a shaft 208 which extends through a bearing block 210 which is mounted to the tank shelf 211 (shown in dashed lines). The shaft 208 extends to a crank arm 212. As the crank arm 212 rotates in a clockwise direction (looking from top to bottom along the rotational axis) it repeatedly engages a drive block 214. The conveyor 216 includes a dog-type system that moves racks containing wares through the machine on tracks 218 in a stop and go fashion with every rotation of the crank arm 212. The dogs 220 are attached to a cradle 222 that is suspended below the tracks 218 on four plastic slider blocks 224. The cradle is made to oscillate back and forth in the direction of arrow 226 by the rotating crank arm 212 and drive block 214, propelling the racks forward on every forward stroke of the cradle 222. The drive block 214 runs in a channel formed by welding two L-shaped brackets together.
Anti-jam prevention is accomplished in the above-described prior art arrangement by mounting the entire drive motor assembly 202 on a pivot. The drive motor assembly 202 is mounted laterally to a movable motor mount 204. The location of the drive motor assembly 202 is normally fixed by use of a die spring 228 which exerts a force sufficient to prevent pivoting under normal, acceptable operating conditions. When the cradle 222 encounters a jam situation, the crank arm 212 is prevented from rotating, causing the drive motor assembly 202 to pivot in a counterclockwise direction (looking from top to bottom along the rotational axis) against the force of spring 228 opening the contacts of an anti-jam switch 230. When opened, the anti-jam switch 230 removes power from a contactor that then opens and removes power to the drive motor. The sensitivity of when the system trips is determined by setting of the die spring 228 and the setting of the anti-jam switch 230.
The above-described anti-jam arrangement may not operate properly if power to the drive motor is hooked up in reverse polarity, causing the drive motor to run counterclockwise instead of clockwise (looking from top to bottom along the rotational axis). When this type of misconnection occurs the drive motor assembly attempts to rotate clockwise when a jam situation occurs. Because such clockwise rotation is not possible, the anti-jam switch will not be activated, potentially resulting in damage to the drive arrangement. Further, even when powered for proper rotation, in a jam situation, due to the time necessary for the drive motor to come to a stop, excessive forces in the arrangement can potentially result in damage to the drive arrangement.
A second potential problem with such warewashers is the build up of excess wares at the outlet end of the warewasher when kitchen personnel fail to remove cleaned wares in a timely fashion. The ware receiving table at the outlet end may include sidewalls and an end wall which prevents wares from tumbling onto the floor. However, if the wares are not removed quickly a back-up can occur in which wares exiting the warewasher may begin to collide with non-removed wares which are abutting against the end wall. This back-up type jam can result in undesired damage to the wares. Attempts to address this type of jam condition include the use of a table limit switch at the end of the ware receiving table which is triggered when wares exiting the warewasher reach the end of the table. Triggering of the switch then cuts power to the drive motor. However, some operators do not use the limit switch option, and instead attempt to rely on the anti-jam switch described above, which includes its own set of problems as previously noted.
Accordingly, it would be desirable to provide a warewasher jam detection system which addresses the aforementioned problems.
In one aspect of the present invention, a warewasher jam detection system includes a conveyor drive arrangement having a drive motor assembly including a drive motor and an output shaft, and a rotatable slip clutch including an input side operatively connected for rotation by the drive motor assembly output shaft, an output side of the rotatable slip clutch operatively connected for driving a conveyor. At least one sensor is provided for producing an output indicative of rotation/non-rotation of the output side of the rotatable slip clutch, wherein non-rotation of the output side during rotation of the input side indicates a jam condition. Preferably the sensor is a non-contact type sensor such as a magnetic sensor, optical sensor or proximity sensor. A controller may be provided for receiving the sensor output signals and identifying a jam condition based upon the same, such that the controller can responsively stop the drive motor.
In one preferred arrangement the system may include at least a first sensor and a second sensor for detecting rotation/non-rotation of the output side of the rotatable slip clutch, with a defined spacing between the first and second sensors. First and second sensor tripping elements are positioned to the output side of the slip clutch, each positioned for tripping the first and second sensor when aligned therewith respectively. A spacing between the first and second sensor tripping elements is different than the defined spacing of the first and second sensors for preventing simultaneous tripping of the first and second sensors.
Still a further aspect of the invention provides a method of detecting a jam condition in a warewasher including a drive motor for driving a conveyor, where the method involves providing a slip clutch between the drive motor and the conveyor. A slip threshold of the slip clutch is set at a level to identify jam conditions and a sensor arrangement is provided for producing an output indicative of a movement state of an output side of the clutch. A jam condition is identified based upon the output produced by the sensor arrangement.